The present invention relates to diagnostic ultrasound systems. In particular, the present invention relates to method and apparatus for acquiring and processing ultrasound data streams to reduce the bandwidth of the data without deteriorating the performance of the beamformer, and to share the bandwidth between two or more data streams belonging to different beams in multi-line acquisition.
FIG. 3 illustrates a typical configuration of a receive beamformer 200. Digitized channel signals are input to a number of identical signal processing devices (beamformer ASICs) 202-206, that are interconnected in a beamsum pipeline. The ASIC 202 performs a partial beam formation of channels 1-8. The partial beamsum 208 is then input to ASIC 204 and added to the partial beamsum of channels 9-18 within ASIC 204. This process is continued down the beamsum pipeline until the final beamsum 210 is coming out of the last ASIC 206 in the chain.
For a time-delay beamformer, such as receive beamformer 200, the data may typically be 20 bit wide and have a data rate of 40 MHz per beam, i.e. 800 Mbit/s data bandwidth. With simultaneous reception of parallel beams, or multi-line acquisition (MLA), this data rate is multiplied by the number of parallel beams. The cost of the interconnect infrastructure within the ultrasound system increases with data bandwidth, as more pins are required on integrated circuits for signal processing, more pins on circuit board connectors, or a faster clock rate of the data paths.
FIG. 4 illustrates the contents of the partial beamformer ASICs 202-206 of FIG. 3. An input data rate (sampling rate) of 40 MHz is assumed, although other data rates may be used. Each channel 1-8 is processed through a per-channel beamformer 212-216. The per-channel beamformers 212-216 perform per-channel beamforming (time delay and optionally per-channel amplitude weighting).
The output from the beamsummer 218, the partial beamsum 208, is then passed through a low-pass anti-aliasing filter 220 that cuts off frequencies above 10 MHz, reducing the bandwidth of the signal. Data output from the low-pass anti-aliasing filter 220 is represented as data stream A 224, following a sequence of samples A1 A2 A3 A4 A5 . . . and so on. A decimator 222 then reduces the data rate by throwing away every other sample of the data stream A 224 to produce data stream B 226, giving the sample sequence of A1 X A3 X A5 X . . . and so on. The X's in data stream B 266, and all subsequent data streams discussed herein, represent data samples which have been thrown away. Data stream B 226 is then summed by summer 228 with a cascading input 230. The cascading input 230 may be supplied through an optional delay line 232 to allow for summing with a subsequent device. The delay line 232 may not be required for certain beamformer architectures.
Alternatively, the cutoff-rate of the anti-aliasing filter 220 may be 20 MHz/n, wherein n=1,2,3,4 . . . , allowing for a data output rate of 40 MHz/n by throwing away (n-1) samples for every sample that is retained. A larger value of n results in a greater reduction of the data rate. Unfortunately, the maximum usable frequency of the receive beamformer 200 becomes reduced by a factor n, for example, from 20 MHz to 20 MHz/n.
Thus, a system and method are desired to acquire data with a maximum frequency which is not limited to one-half the data sampling rate of the output stream that addresses the problems noted above and others previously experienced.